Reland of "Apply Shelf/Dock opacity animations for the Material Design style."

ash/shelf/shelf_view.h

Index: ash/shelf/shelf_view.h
diff --git a/ash/shelf/shelf_view.h b/ash/shelf/shelf_view.h
index 8af3d1e4882ceaef8a3df332948e784c3b0fe990..65870608db8a3d67d2ba7f0a5b70b74914636a8b 100644
--- a/ash/shelf/shelf_view.h
+++ b/ash/shelf/shelf_view.h
@@ -159,6 +159,9 @@ class ASH_EXPORT ShelfView : public views::View,
                                Pointer pointer,
                                bool canceled);
 
+  // Updates the background for the shelf items.
+  void UpdateShelfItemBackground(int alpha);
+
   // Return the view model for test purposes.
   const views::ViewModel* view_model_for_test() const {
     return view_model_.get();